This invention relates generally to high frequency filter circuits and particularly to intermediate frequency (IF) filter circuits for use in connection with direct broadcast satellite (DBS) television receivers.
DBS television generally involves FM modulating a plurality of baseband television video and sound signals onto an "uplink" microwave carrier which is directed at one or more satellites and transmitted back at about 12 gigahertz to permit reception at remote points with suitable apparatus. Individual microwave receivers are coupled to suitable dish antennas and are generally located close to the antenna in environmentally protected enclosures. The outside receiver unit comprises an RF amplifier, a high frequency oscillator and a mixer for converting the 12 gigahertz signal into a signal of more manageable frequency, such as for example a 1 gigahertz IF frequency. The IF frequency containing a number of television channels, is supplied to a converter located in the house, where it is amplified, filtered and the desired baseband television signal recovered by detection of the FM modulation. The recovered baseband television signal is then processed and may be fed in either composite or RGB format to a television monitor or it may be remodulated onto a suitable carrier frequency for presentation to the radio frequency tuner input of a conventional television receiver. The remodulated signal is generally on carriers corresponding to television VHF channels 3 or 4, as with most video cassette recorders and video games.
Since all of the described equipment, except for the television receiver, is additional there is an understandable desire to keep its cost low to permit the direct broadcast service without placing an undue economic burden on subscribers. It is also highly desirable to minimize the size of the added equipment, which in most instances is separate from the television receiver. Since obvious goals in all such apparatus are uniformity in performance and ease of manufacture, it is desirable to use simple circuits that are readily aligned and that are stable in operation.